Device in grinding apparatus for vegetable or fibrous material

ABSTRACT

The invention relates to a grinding apparatus for vegetable or fibrous raw material comprising a casing surrounding grinding discs mounted rotatably relatively one another and means for supplying steam under high pressure, so called primary steam, together with the raw material into the casing, where the introduced material is ground in the interspace between the grinding disc, the ground material being discharged from the casing through an outlet controlled by an adjustable valve. In order to keep the quantity of steam escaping from the casing along with the discharged produce, the outlet valve is devised to be actuated by the pressure in the casing via a control device responsive to said pressure which is determined, in addition to the action of the primary steam, by secondary steam supplied separately through a conduit to the casing.

States Patent [1 1 Ullit Reinhall DEVICE 1N GRINDING APPARATUS FOR VEGETABLE OR FIBROUS MATERIAL [76] Inventor: Rolf Bertil Reinhall, 16,

Killingevagen S-l8l, 64 Lindingo 3, Sweden [22] Filed: Oct. 20, 1972 [21] Appl. No.: 299,259

[52] US. Cl 241/245, 241/38, 241/65 [51] int. Cl. 8020' 7/02, B020 7/17 [58] Field of Search 241/38, 65, 8, 41, 245

[56] References Cited UNITED STATES PATENTS 2,396,587 3/1946 Lowgren et al 241/65 3,661,328 5/1972 Leask 1. 241/65 X Primary EraminerRoy Lake Assistant Examiner-E. F. Desmond Attorney, Agent, or Firm-Eric Y. Manson Nov, 12, 1974 [5 7 ABSTRACT The invention relates to a grinding apparatus for vegetable or fibrous raw material comprising a casing surrounding grinding discs mounted rotatably relatively one another and means for supplying steam under high pressure, so called primary steam, together with the raw material into the casing, Where the introduced material is ground in the interspace between the grinding disc, the ground material being discharged from the casing through an outlet controlled by an adjustable valve. In order to keep the quantity of steam escaping from the casing along with the discharged produce, the outlet valve is devised to be actuated by the pressure in the casing via a control device responsive 'to said pressure which is determined, in addition to the action of the primary steam, by secondary steam supplied separately through a conduit to the casing.

2 Claims, 1 Drawing Figure- DEVICE IN GRINDING APPARATUS FOR VEGETABLE OR FIBROUS MATERIAL FIELD OF THE INVENTION This invention relates to a device in grinding apparatus for vegetable or fibrous material.

More particularly this invention relates to a grinding apparatus for vegetable or fibrous raw material which comprises discs mounted rotatably relatively one another in a casing, a superatmospheric pressure being maintained in said casing by means of steam primary steam which together with the raw material is introduced into the interspace between the grinding discs,

an adjustable control valve being provided in an outlet fromthe casing'for the ground produce.

In order to obtain good heat economy it is necessary to limit as much as possible theamount of steam which escapes along with the ground material through the outlet valve from the casing held under pressure. An important factor in this connection is that the treated material leavingthe grinding members must not accumulate in the casing in such a degree as to cause stoppage of the apparatus.

THE, PRIOR ART It is known for this purpose to apply manual adjustment of so-called exhaust valves to their minimum passage opening or periodically operating so-called sluice valves with the lowest operating frequency, in which adjustments the operator, however, forpractical reasons operates with some safety margins which result in an unnecessarily great discharge of steam and thus undesired heat consumption.

OBJECTS OF THE. INVENTION One main object of the invention is to provide a device by means of which the heat consumption can be maintained at a minimum without any risk of clogging of inner portions of the apparatus.

Another essential object of the invention is to determinethe dwell time of the material in the interspace between the grinding discs in order thereby to attain best properties in thefinal product.

MAIN FEATURES OF THE INVENTION 7 ADVANTAGES OF THE INVENTION The invention, ensures that the ground material is sluiced out through'the outlet or discharge valve as its grinding treatment in the apparatus is finished, together with a minimum quantity of steam. If produce is collecting temporarily in front of the valve, the pressure will exceed the highest pressure level defined by the secondary steam supply because said level is lower than the pressure level of the primary steam supplied to the inlet side to the grinding interspace. Steam under the higher pressure continues, of course, to pass through the interspace together with fresh material to be ground. This results in that the regulator reacts to the increased pressure in such a manner that the control valve opens and permits increased escape of produce. If, to the contrary, the pressure in the casing drops below the adjusted maximum value for the secondary steam, the outlet or discharge valve receives an impulse in opposite direction so that the discharge area or operating frequency of said valve is reduced.

The degree of disintegration or the intended properties of the ground pulp depend on the duration of stay of the material between the grinding discs. The longer the duration of stay, or dwell time, the greater the wearing of the grinding surfaces assuming that the condition remains the same. According to the invention, it becomes possible to compensate for this increased dwell time in a very simple manner by increasing the pressure difference between the two supplied steam currents.

BRIEF DESCRIPTION OF THE DRAWING Further objects and advantages of the invention will become apparent from the following description, considered in connection with the accompanying drawing, which forms part of this specification and which diagrammatically shows a grinding apparatus embodying the features of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, reference numeral 10 denotes a stock vessel for the raw material,- such as wood in disintegrated state or so-called wood chips. The raw material is introduced by a feeding device 12, such as a screw conveyor, into a' receptacle l4 subjected to a steam pressure P1, the feeding device creating a resistance against said pressure. The bottom of the receptacle 14 is in direct communication witha grinding apparatus l8of the disc type by means of conveyor screw 16, said apparatus comprising a closed casing 20 within which are mounted a stationary grinding disc 22 and a rotatable grinding disc 28 mounted on a shaft 24 in the frame 26. The raw material supplied by the conveyor screw 16 is fed through a central aperture 30 at the inner peripheryof an interspace3l formed between the two grinding discs 22, 28. Simultaneously, steam under the pressure Pl, hereinafter also denominated as primary steam, follows, and thus also passes through the interspace 31 together with the wood material when this is ground between the grinding discs and conveyed radially outwards into the surrounding 'casing 20. Said casing 20 has at its bottom a discharge or outlet 32 controlled by an exhaust valve 34 capable of adjusting the passage area of the outlet.

The valve 34 is adjusted by means of a mechanism or servo motor 36 e.g. of the cylinder and piston type and controlled by a control device or regulator 38 which in turn via a conduit 39 and a pressure sensing instrument 40 is continually actuated by the steam pressure pre- From a pressure source not shown steam is supplied through a pipe 54 into the receptacle 14. Provided in this pipe is a pressure reducing apparatus 56 by which the steam pressure is adjusted to any slightly lower, although constant value which thus becomes the steam pressure Pl for the primary steam. This steam flows together with the raw material through the interspace 31 between the grinding members 22 and 28 out into the casing 20, the flow speed ofsaid steam thus varying in accordance with the rate of discharge of finished material and escape of steam through the valve 34. This discharge in turn affects the dwell time of the material in v the grinding interspace 31 and consequently also the quantity of energy supplied to the material by the grinding apparatus.

According to the invention, the casing of the grinding apparatus is provided with a separate inlet pipe 58 forsteam under the pressure P2, hereinafter also denominated secondary steam. Provided in the pipe- 58, which may branch off from the pipe 54, is a control instrument or regulator 60 which adjusts the steam pressure P2 to a value which is lower than the steam pressure P1. The pressure difference which is adjustable may amount to some superatmosphe-ric atmospheres. Provided in the inlet or'pipe 58 may in addition be a valve 62 by means of which, e.g., duringthe initial adjusting of the grinding apparatus to predetermined operating conditions the supply of secondary steam can be determined so as to cause the exhaust of steam through the valve 34 together with treated material to remain at adesired minimum value.

The interspace 31 between the two grinding discs 22, i

28 in the grinding apparatus 18 of the disc type is in a manner known per se adjustedto a desired magnitude with regard to the properties which are desired to be obtained in the ground produce. This adjustment can be controlled by a servo motor mechanism of the known type shown and described, e.g., in the US. Pat. No. 2,891,733. The active grinding surfaces of the grinding discs are formed by elongated grooves and projections spaced from one another in a manner known per se.

According to the invention, the exhaust valve 34 always provides such a discharge area that it cannot be blocked by clogging of finished product under discharge through the interspace 31. Within the grinding casing 20 at the sideof discharge from the interspace between the grinding discs prevails a pressure which is adjusted to a desired maximum value P2. In case ground produce is accumulated in the valve 34 so that it tends to become blocked, the quantity-of steam escaping from the grinding casing 20 is also reduced. The pressure P2 which is controlled by the regulator 60 will then be exceeded by steam current under the higher pressure P1 and thus will continue to pass together with fresh grinding material through the interspace between the grinding discs. The result will be an increase of pressure in the grinding casing to which increase the regulator 38 reacts so that the mechanism 36 transmits I an impulsecausing increase of the discharge opening of the valve 34. The accumulated ground material is now in a position to stream out so that the pressure in the grinding casing 20 returns to the value P2. A similar actuation of the valve 34, although in the opposite direction, takes place when its discharge opening sluices out too much material so that the pressure drops below the value P2.

- The pressure difference Pl P2 becomes its determinating factor for dwell time of the produce between the grinding members andconsequently also for the degree of disintegration thereof into fibres or fibrilles. On the other hand,'material may be accumulated in the grooves of the grinding discs depending on variations in the dry content, particle size, resin content etc ofthe raw material, which will result in a reduction of the quantity of steam. This may occur also when a constant quantity of material to be ground passes through the grinding interspace with long dwell time. Unless secondary steam is supplied, the result would be that the pressure in the casing 20 decreases in spite of unchanged quantity of finally ground material leaving the grinding interspace. As a matter of fact, the discharge area of the exhaust valve is determined by the pressure prevailing in the casing 20 which pressure due to the reduced quantity of primary steam does not reach such a value as may be required to cause the finally ground material to accumulate ahead of the valve 34. The consequence would be a stoppage of the whole apparatus. By supplying secondary steam according to the invention the pressure in the casing required to cause the intended discharge through the valve 34 is ensured.

Obviously, more than two grinding discs may be included in the grinding casing. The grinding discs or members may both-be rotatable, either with various angular velocity, or in opposite directions.

While one more or less specific embodiment of the invention has been shown and described, it is to be understood that this is for purpose of illustration only, and that the invention is not to be limited thereby, but its scope is to be determined by the appended claims.

What is claimed is:

l. A grinding apparatus comprising:

a. a housing; j

b. a pair of grinding discs arranged within said housing defining between them a grinding space for defibering and refining fibrous vegetable material and the like:

c. means for introducing the raw material into said grinding. space;

d. means for introducing a primary current of steam having a predetermined degree of pressure into said grinding space jointly with the raw material;

e. an outlet for the discharging of the heated material and steam from said housing;

f. means for introducing a secondary current of steam having a predetermined lower pressure than the pressure of said primary steam current directly into the housing;

g. valve means responsive to fluctuations in the pressure in said housing for regulating the rate of discharge of treated material and steam from said outlet.

2. Apparatus according to claim 1 in which said secondary steamcurrent is controlled to maintain a predetermined pressure differential between said primary steam current and said secondary steam current. 

1. A grinding apparatus comprising: a. a housing; b. a pair of grinding discs arranged within said housing defining between them a grinding space for defibering and refining fibrous vegetable material and the like: c. means for introducing the raw material into said grinding space; d. means for introducing a primary current of steam having a predetermined degree of pressure into said grinding space jointly with the raw material; e. an outlet for the discharging of the heated material and steam from said housing; f. means for introducing a secondary current of steam having a predetermined lower pressure than the pressure of said primary steam current directly into the housing; g. valve means responsive to fluctuations in the pressure in said housing for regulating the rate of discharge of treated material and steam from said outlet.
 2. Apparatus according to claim 1 in which said secondary steam current is controlled to maintain a predetermined pressure differential between said primary steam current and said secondary steam current. 